There are presently a large number of patents relating to ink drop printers which break each stream of ink, the streams being of substantially circular cross-section, into one controlled stream of droplets of ink. The present invention is probably the first design for an ink drop printer which breaks one stream of ink, in the form of a ribbon, into many side by side rougly parallel but controlled streams of droplets.
The idea of using electrostatic control sites on a rotating drum surface to control multiple streams of ink, each forming controlled droplet streams at or before the drum, is shown in U.S. Pat. No. 4,138,686 and in an application concurrent with this application. However the sites were aligned along parallel rings around the drum, making the spacing between droplet streams equal to the center to center spacing between sites and to the spacing between stream orifices. However, in the current invention the sites can be located more closely together than typical orifices of former art, and can be located, if desired, on helical paths. Therefore, the axial spacing between sites, and thus the spacing between droplet stream origins, can be far less than the center to center spacing between sites, if the sites are on helical paths. The apparent origin of each stream is somewhat blurred, because droplets may be released over a small range of rotation angles.
Advantages of the present invention over former art include the following. The one mil circular cross-section orifices necessary in former art are difficult to produce. Also they must be spaced further apart than the drum sites of the current invention. The ribbon of ink is easier to produce, since optically flat surfaces and accurate spacers, long available, can be employed as a single unit to replace the multiple orifices of former art.
The helically located sites allowing closely spaced controlled droplet streams give better definition to output than formerly possible with stationary stream origins and droplet paths controlled only in one direction (parallel to the output motion). Parallel control can be achieved in the current invention by timing the release of the droplets. It can be used to correct for output means positioning, and to correct for unequal travel times from the droplet stream origins to the output, due to unequal drag effects.
Site wiring has been improved ans simplified, since the same logic may now be used to control correspondingly positioned sites on the curved surface of each of a number of wedges. The wedges in combination form the whole drum. Only one wedge or two parts of wedges adding to one wedge or less are controlling ink segments at any one time. Thus the control instructions although repeated, due to parallel wiring, on all wedges actually only apply to the currently active contacting wedge portions.
Ionically conducting ink can be used in any of the preferred embodiments of this invention, since charging of droplets is not essential. Thus simply produced inexpensive ink can be electrostatically controlled as to flight path and can impact on a densely spaced matrix at the output.